The present invention relates to the destruction of contaminants entrained in a fluid stream, particularly to the destruction of non-biological particulate matter or biological contaminants such as spores, bacteria or viruses entrained in this fluid stream, particularly in a gas stream such as contaminated air. As used herein the term “destroy” broadly means killing or otherwise converting all or some of the contaminants within the fluid to a state which is less harmful to humans, animals or other organisms or devices present in environments requiring or benefited by a purified fluid. The present invention also is directed to destroying or altering chemical species which are entrained in a fluid stream, and particularly a contaminated air stream. As used herein the term “alter” broadly means any change in the chemical structure which results in the chemical being less harmful to humans, animals or other organisms or devices present in environments requiring or benefited by a purified fluid. In one aspect, the present invention is directed to destruction or altering of biological and/or chemical contaminants (sometimes referred to herein as “agents”) as occurs by passage of the fluid stream through a compressor, for example a Roots-type or positive-displacement compressor, a centrifugal or high pressure fan centrifugal compressor, etc. In a particularly contemplated embodiment of the present invention, some of the heat imparted to the fluid stream during passage through the compressor is recovered from the fluid stream outflow downstream of the compressor and fed back to add heat to the compressor, thereby reducing the energy requirements for destruction of agents or chemical species through the compressor, as well as optionally producing a final fluid stream temperature more closely matching human and/or machine-tolerable temperatures, ambient temperatures, or the like, if needed for the particular application.
In the world today pathogens, viruses, bacteria and chemical species in the air either naturally or deliberately placed there are becoming an increasing health risk. Many bacteria are developing resistance to antibiotics and fewer new antibiotics are being developed. Outbreaks of airborne infections have been reported in hospitals. Clearly a better way of dealing with this health threat is needed. Terrorists have used bacteria and chemical species in attacks. Anthrax contaminated a U.S. Capital office building. The defense today against these species is typically HEPA filters capable of trapping particles as small as 0.3 microns. However, HEPA filters must be changed frequently, and used HEPA filter materials in some cases must be treated as hazardous waste. Furthermore, the performance of HEPA filters is dependent on their installation, and on the care taken in their replacement. Thus, for example, poor installation can result in the passage through the filtering system of unfiltered air, defeating the purpose of the filtration system and, in a worst-case scenario, leading to human sickness or death from contaminated air, e.g., air contaminated by biohazardous agents or chemical agents.
As an alternative to HEPA filtration, biological and/or chemical agents may be destroyed or altered rather than removed by filtration. In this regard, studies have shown some bacteria species can be destroyed at temperatures as low as 100° C. At temperatures approaching 250° C. almost all pathogens, viruses and bacteria are destroyed. At somewhat even higher temperatures, chemical species are destroyed or altered by thermal decomposition processes. Thus, sufficiently high temperatures may be used to destroy and/or alter biological and/or chemical agents.
While high temperatures may be used to destroy or alter such biological and/or chemical agents as described above, the method or system by which such high temperatures are generated is of utmost importance. Such heating methods and systems are useless unless they can demonstrate commercial viability. Thus, if the heating method or system has high power consumption and/or inordinately long processing times (i.e., time of exposure of the fluid stream to the high temperature), the method/system would simply not be commercially viable.
One possible method for high temperature destruction or altering of biological and/or chemical agents in a fluid stream is by passage of a fluid stream through, e.g., a positive-displacement compressor such as a Roots-type compressor as is described in U.S. Pat. No. 7,335,333, the disclosure of which is incorporated herein by reference, wherein it is disclosed how such passage through the compressor destroys bacteria, bacterial spores, and other biological agents in the fluid stream. As disclosed in the '333 patent, upwards of 99.9% of Bacillus glonigii (Bg) spores, an anthrax stimulant, where killed by compressive heating to about 200° C. in a single pass through a Roots-type positive displacement compressor.
Although methods based on passage of a fluid stream through a positive displacement compressor such as a Roots-type compressor as described in the '333 patent are desirable for the reasons set forth above, it would be advantageous to further improve the energy efficiency of these methods. For example, it would be particularly advantageous to use some of the heat contained in the fluid stream at the outflow end of the positive-displacement compressor or downstream of the positive-displacement compressor to lower the energy costs of operating the compressor. For example, recovery of some of the heat of the fluid in the outflow stream could be redirected back to the compressor (e.g., to heat the compressor body itself and/or the inlet fluid to the compressor, etc), thereby lowering the amount of additional heat required to be generated by the compressor to obtain the necessary kill/decontamination conditions in the compressor. Such methods would have an additional energy benefit of reducing the energy requirements for lowering the temperature of the output fluid stream to a range suitable for exposure to humans, machinery, or other end uses, as required. In the absence of removal of heat from the sterilized heated fluid outflow stream, depending on the application, this stream must be cooled prior to its introduction into spaces occupied by, e.g., humans, animals or other organisms or devices as discussed above. By directly removing some of the heat from this fluid output flow stream, energy input that would otherwise be required to cool this stream may thus be avoided.
There therefore exists a need for improved, energy-efficient methods and systems for destroying or altering biological and/or chemical agents in a fluid stream.